丙烯酸十八酯共聚物的结晶和熔融行为研究

CRYSTALLIZATION AND MELTING BEHAVIOR OF POLY(n-ALKYL ACRYLATE-co-OCTADECYL ACRYLATE)S

合成了丙烯酸酯(AAn,n为侧链碳原子数)均聚物(PAAn)以及AA18与其同系物的无规共聚物((P(AA18-co-AAn)),并研究了P(AA18-co-AAn)的结晶和熔融行为.结果表明,在AA18与结晶同系物AAn(n=10,12,14,16)的共聚物中,结晶度(Xc)随AA18含量的增加而增大,相应的熔程先增加后下降,存在一个最大值;P(AA18-co-AA14)和P(AA18-co-AA16)的相对结晶度(Xc/Xcmax)受AA18含量影响不大,而P(AA18-co-AA10)和P(AA18-co-AA12)的Xc/Xcmax随AA18含量增加先下降后上升;随着AA18与共聚组份侧链碳原子数差别的增大,熔程的最大值明显增加.在AA18与非结晶同系物AAn(n=4,6,8)的共聚物中,Xc和Xc/Xcmax值随AA18含量的增加而增大,而Xc/Xcmax值随AAn侧链碳原子数的增加而减少,共聚物熔程的最大值差别不大.

A series of poly（n-alkyl acrylate）s （PAAn） and poly（octadecyl acrylate-co-n-alkyl acrylate）s （P（AA18-co-AAn）） （n, the side chain carbon number） were synthesized with AIBN as initiator at 60℃ for 24 h in nitrogen atmosphere. The molecular weight of the polymers and the polymer dispersity index were measured with gel permeation chromatography （ GPC）. The thermal behaviors of PAA n and P （ AA18- co-AA n ） were studied by differential scanning calorimetry （DSC）.The results manifest that, for homopolymers, there is a gradual increase of fusion heats and melting points with the side-chain carbon number ranging from 10 to 20, because more units of methylene enter into the crystal lattice for PAAn with longer side chains length. At the same time, the melting endothermal peak of PAA n was not detected in DSC running as the n was less than 10, which meant that 10 was the critical side chain carbon number for the discrimination of crystallizable and non-crystallizable PAAn. For copolymers of AA18 with crystalline homologous AAn （ n = 10, 12, 14, 16） series, the crystallinity （ Xc ） of copolymers was between the values of the corresponding homopolymers, and it increased with increasing the content of AA18, and the corresponding melting ranges had a maximum value at certain AA18 content. The value of extent of equilibrium crystallinity （Xc/Xcmax ） of P（AA18-co-AA14） and P（AA18-co-AA16） changes little with increasing content of AA18,because the side chain carbon number of monomers has little difference and the affection of the other side chain is small. While the Xc/Xcmax of P（AA18-co-AA10） and P（AA18-co-AA12） increases at first and then decreases. The more difference of side chain carbon numbers （18/12,18/10） led to the interactional disturbing effect, and many defects would occur during crystallization. At the same time, the shorter side chain length of AA10 and AA12 decreased the crystallizing ability obviously resulting in much less Xc. For the copolymers of AA18 with non-crystalline homologous AAn （n = 4,6,8） series,both Xc and X increased with increasing content of AA18, since AA18 was the only crystallizable component. With increasing the side chain carbon number of non-crystalline homologous AAn series （n = 4,6,8） of the same AA18 mole fraction, the values of Xc/Xcmax decreased, while the maximum values of melting range almost kept constant.