Effect of Linear and Ring-like Co-units on the Temperature Dependence of Nucleation and Growth in Ⅱ-Ⅰ Phase Transition of Butene-1 Copolymers

The phase transition from tetragonal form II to hexagonal form I was studied for the butene-1/ethylene and butene-1/1,5- hexadiene random copolymers, which have comparable molecular weight but distinct linear ethylene and ringlike methylene-1,3- cyclopentane （MCP） structural co-units, respectively. It is known that this solid phase transition follows the nucleation-growth mechanism, so the stepwise annealing protocol was utilized to investigate the influences of co-units on the optimal nucleation and growth temperatures. Compared with optimal nucleation and growth temperatures of-10 and 3 5 ℃, respectively, in polybutene-1 homopolymer, two butene-1/ethylene copolymers with 1.5 mol% and 4.3 mol% co-units have the slightly lower optimal nucleation temperature of-15 ℃ but much higher optimal growth temperature of 50 ℃. Clearly, the effect of ethylene co-unit is more significant on varying optimal temperature for growth than for nucleation. Furthermore, when the incorporated co-unit is ringlike MCP, the optimal nucleation temperature is -15 ℃ for 2.15 mol% co-units, the same with above BE copolymers, but -13 ℃ for a very low concentration of 0.65 mol%. Interestingly, the optimal growth temperature of butene-1/1,5-hexadiene copolymers with 0.65 mo1%-2.15 mol% MCP co- units increases to 55 ℃, which is also independent on co-unit concentration. These obtained values of optimal temperatures provide crucial parameters for rapid II-I phase transition.

Crystallization and Phase Transition of 1-Butene Copolymers with Distinct Cyclic Co-Units

The dimethylpyridylamidohafnium catalyst was used to synthesize 1-butene/cyclohexene and 1-butene/vinylcyclohexane random copolymers,which have extra six-membered cyclic co-units in main chain and side chain,respectively.For the obtained copolymers of different incorporations,the crystallization from amorphous melt and the solid phase transition from tetragonal to trigonal phases were investigated with differential scanning calorimetry.Both of the incorporated cyclic co-units decrease the crystallization kinetics,but the presence of cyclohexene keeps the melting temperature of copolymers constant.Interestingly,the strong memory effect of crystallization can appear at the elevated temperature even above the equilibrium melting temperature,as the content of co-units was increased.The 1-butene/vinylcyclohexane copolymer with 1.52 mol%co-units exhibits a rather strong memory effect with the broad Domain Ila width of 43℃and the crystallization temperature raising of 24℃.Furthermore,the transition of tetragonal phase into trigonal phase was also explored for different co-units and incorporations.It was found that both of the cyclohexene co-units and vinylcyclohexane co-units effectively slow down the kinetics of phase transition.However,the vinylcyclohexane co-units have a much higher efficiency in suppressing phase transition than the cyclohexene co-units,where 0.53 mol%vinylcyclohexane can com-pletely stop phase transition within 1320 h.Considering the fact that copolymers with vinylcyclohexane co-units actually have lower glass transition temperatures,it was indicated that the suppression of phase transition is also largely influenced by the steric co-units in the side chain for the helical and positional adjustments,not only by the segmental mobility.

Self-nucleation Effect of Crystallization with Various Nucleating Agents

In this work,the self-nucleation effect on crystallization was studied for polypropylene with various nucleating agents.The talc was employed to accelerate crystallization of monoclinic α-crystallites,while N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide TMB-5 was used to accelerate the crystallization kinetics and also induce formation of trigonal β-crystallites.To induce self-nucleation effect,the occurrence criterion was assessed by the transition temperatures from various domains and the available temperature width.More importantly,the resulting influences of self-nucleation effect were quantified by the change of crystallization kinetics and the potential polymorphism variation.It was found that the α-nucleating agents of talc broadened the temperature window for inducing Domain Ⅱ by elevating the transition temperature from Domain Ⅰ to Domain Ⅱ.Although β-nucleating agent(β-NA)of N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide TMB-5 elevated cooling crystallization temperature obviously,the temperature window for Domain Ⅱ was narrowed.It should be emphasized that in presence of β-NA TMB-5,the self-nucleation effect enhances the crystallization of α-crystallite,which show the competition with β-NA TMB-5.At last,the ternary PP/talc/TMB-5 blend was prepared with the same amounts of α-NA talc and β-NA TMB-5 and it exhibits a similar self-nucleation effect of crystallization,indicating the dominant role of β-NA TMB-5.

Effect of Olefin-based Compatibilizers on the Formation of Cocontinuous Structure in Immiscible HDPE/iPP Blends

In this work,the formation of cocontinuous structure in immiscible high density polyethylene/isotactic polypropylene(HDPE/iPP)blends was investigated for various olefin-based compatibilizers of distinct molecular architectures,including ternary random copolymer EPDM,olefin block copolymer(OBC),polypropylene-based OBC(PP-OBC),ethylene/a-olefin copolymer(POE),bottlebrush polymer poly(1-dodecene),and comb-like poly(propylene-co-high a-olefin)(PPO).The scanning electron microscopy results show that after adding OBC,PP-OBC,and POE copolymers,the finer droplet-in-matrix morphologies were obtained in 70/30 HDPE/iPP blend.Interestingly,for 70/30 HDPE/iPP blend with just 5 wt%of PPO copolymers,the phase inversion from droplet-in-matrix to cocontinuous morphology can be observed.It was proposed that the development of cocontinuous morphology contained the following steps:(1)in terfacial saturati on of compatibilizers and droplet deformation,(2)droplet-droplet coalesce nee,(3)continuity development,and(4)the formation of dual-phase con tinuity.Among the diverse copolymers studied in this work,PPO copolymer can be easily removed out of the interface during droplet coalescence and stabilize the curvature of minor fiber phase,facilitating the formation of cocontinuous morphology.In contrast,other olefin-based compatibilizers(EPDM,OBC,PP-OBC,and POE)exhibit the distinct steric repulsion effect to prohibit droplet coalescence.Moreover,the cocontinous interval varies with the compatibilizer architectures.Surprisingly,after adding 10 wt%of PPO copolymers,the cocontinuous interval was greatly broadened from HDPE/iPP range of 45/55-60/40 to that of 40/60-70/30.

Memory Effect of Crystallization in 1-Butene/α-olefin Copolymers

The macromolecular architecture is the crucial factor in determining the arrangement of the ordering structures,which,because of the multiscale feature,may exhibit distinct melting behaviors and induce the so-called memory effect to affect the following recrystallization.Until present,the correlation between the occurrence of memory effect and the intrinsic molecular structure is still far from the comprehensive understanding.In this work,four kinds of 1-butene/α-olefin random copolymers were designed and synthesized using the(pyridyl-amino)hafnium catalyst to introduce the different branches.The branch length was precisely controlled by the specific α-olefin comonomers,which include 1-hexene,1-decene,1-tetradecene,and 1-octadecene,while the branch density was tuned by the incorporation.As expected,the incorporation of α-olefin co-units to poly(1-butene)backbone decreases the non-isothermal crystallization kinetics and the degree of crystallinity.More interestingly,the resulting linear branch can induce the occurrence of memory effect and the threshold concentration of co-units(i.e.,branch density)decreases with increasing the branch length.Based on the results of these 1-butene/α-olefin copolymers with designable branches,a direct correlation with the occurrence of memory effect and the fraction of amorphous region was established,which quantitatively indicates the degree of local segregation of the crystallized poly(1-butene)sequences by theα-olefin co-units.

A Rational Design of Heterojunction Photocatalyst Cd S Interfacing with One Cycle of ALD Oxide

Photo-corrosion is one of the major obstacles for CdS application in wet chemical fields, and atomic layer deposition （ALD） has been proposed as an effective way to suppress the corrosion. Here, prior to ALD coating, CdS, one facilely corrosive photocatalyst, was synthesized via hydrothermal synthesis to access the fundamental corrosion mechanism and the according corrosive sites. X-ray photoelectron spectros- copy （XPS） and X-ray diffraction （XRD） demonstrated that the failure of catalytic decomposition of methylene blue originated from the formation of soluble CdSO4 by oxidizing S2 of as-prepared CdS. High resolu- tion transmission electron microscopy （HRTEM） further identified the active sites in the V-shaped regions ofCdS nanoparticles, confirmed by the simulated electric field distribution. To rationally coat oxides on CdS, the right candidates and their thicknesses have been considered by our tunneling model with trans- fer matrix method based on quantum mechanism, upon which the thickness of protective layer should be less than 0.5 nm to maintain a high tunneling probability, and thus one cycle of ALD TiO2 or AbO3 was proposed to passivate the CdS powder to balance the carrier transportation and corrosion suppres- sion. Based on HRTEM results, we found that the active V-shaped region was covered by ALD oxides （TiO2 or AbO3）. For each case, no soluble CdSO4 has been found before and after photocatalytic reactions based XPS measurements. Importantly, we noticed that with the passivation of one cycle of ALD, the catalyst＇s lifetime was elongated up to 〉14 times higher than that of the as-prepared CdS.

Enhanced Phase Transition in Poly(ethylene glycol) Grafted Butene-1 Copolymers

In the present work,a series of poly(ethylene glycol) grafted polybutene-1 copolymers(PB-g-PEG) were designed and successfully synthesized with reaction intermediate method,of which the branch densities and length could be tuned independently.The branch density varied from 0.39 mol% to 1.23 mol% and the branch length was tuned by employing PEG number-averaged molecular weight(Mn) from 350 Da to 750 Da and 1000 Da.The non-isothermal crystallization and phase transition behaviors of these butene-1 copolymers with varying branches were systematically explored by differential scanning calorimeter.The results first showed that compared with the linear polybutene-1 homopolymer,presence of steric 4-[4-(trimethylsilylalkynyl)-phenyl]-1-butene(TMS) groups suppressed crystallization and phase transition of copolymers.Interestingly,the introduction of long poly(ethylene glycol)(PEG) branches with M_(n)=350-1000 Da not only elevated the peak temperature of the non-isothermal crystallization but also enhanced the Ⅱ-Ⅰ phase transition,with respect to copolymers with TMS groups.Furthermore,the quantitative correlations between phase transition kinetics with the branch parameters(density and length) were explored.It was found that the phase transition presents a non-monotonic trend with increasing branch density and branch length.In this case,the optimal branch density and length obtained were 0.77 mol% and 750 Da,respectively.Employing the small angle X-ray scattering and transmission electron microscopy,a direct correlation between the phase transition kinetics and the long periodicity of separated phase was obtained,which may be due to the increased internal stress and facilitated stress transport.