Taking account of the effect ale heteroatoms iq backbone, this article dealt with the mean-square radii of gyration of polyalkyleneoxides by the approach of matrix algebra in accordance with the rotational isomeric st...Taking account of the effect ale heteroatoms iq backbone, this article dealt with the mean-square radii of gyration of polyalkyleneoxides by the approach of matrix algebra in accordance with the rotational isomeric state model, Numerical calculation with the parameters available in the literatures indicated that the dependence of [S-2] on the molecular weight can be expressed by the general formula: [S-2]=aM(b).展开更多
The mean-square radius of gyration <S^2>,the mean-square dipole moment <D^2>,the mean-square end-to-end distance <R^2> and their temperature coefficients of unsymmetrical disubstituted poly(methylphe...The mean-square radius of gyration <S^2>,the mean-square dipole moment <D^2>,the mean-square end-to-end distance <R^2> and their temperature coefficients of unsymmetrical disubstituted poly(methylphenylsiloxane) (PMPS) chains, as a function of stereochemical structure,confomational energies and length of polymers,were studied by using an improved configurational-confomational statistical method based on the rotational-isomeric-state theory.It is found that the increase in isotacticity of P...展开更多
Crystallization in polymer systems actually is a process that transfers the entangled melts into a semi-crystalline layered structure. Whether or not a chain disentangles may result in different crystallization mechan...Crystallization in polymer systems actually is a process that transfers the entangled melts into a semi-crystalline layered structure. Whether or not a chain disentangles may result in different crystallization mechanism. When compared to the crystal thickness (d(c)), the volume occupied by the chain in the melts i.e., the radius of gyration (R-g), plays a very important role in polymer crystallization. When d(c) less than or equal to R-g, crystallization does not necessitate a chain disentangling. The entanglements are just shifted into the amorphous regions. However, as d(c)>R-g, i.e., as the crystal thickness gets larger than the radius of gyration of the chain in the melt, it becomes necessary for a chain to disentangle. Then a change of crystallization mechanism occurs. Such change has been experimentally observed in the crystallization of poly(I-butene). A change in the crystal morphologies from spherulite to quadrangle, is seen via PLM, as crystallization temperatures increase. Even more, such a change is molecular weight dependent, and shifts to lower temperature as molecular weight decreases. There exists a jump of crystal thickness and crystallinity associated with morphological change, as seen via SAXS. A change of crystallization kinetics and crystallinity is further evidenced via dilatometry. The unique feature of P1b crystallization has been discussed based on the radius of gyration of chain in the melt (R-g), and very good agreement is obtained.展开更多
This work deals with the dependence of the z-average mean-square radius of gyration (<R 2> z) on the degree of branching(DB) for highly branched copolymers made from the one-pot cocondensation of AB 2 and AB mon...This work deals with the dependence of the z-average mean-square radius of gyration (<R 2> z) on the degree of branching(DB) for highly branched copolymers made from the one-pot cocondensation of AB 2 and AB monomers. A new expression of the degree of branching has been derived. The DB monotonously increases with increasing A group conversion and the fraction of AB 2 monomers. The value of DB calculated in accordance with our formula is lower than that given by Frey and coworkers. Howerver, when the reaction approaches completion, our expression of the degree of branching degenerates into the equation reported by Frey. Furthermore, the z-average mean-square of gyration of the resulting copolymer in the Θ state has been derived on the basis of the classical work developed by Stockmayer, Gordon, Li and Ba. The relationship between DB and <R 2> z is illustrated by numerical results. The z-average mean-square radius of gyration of the copolymer with a certain weight-average molecular weight monotonously decreases with increasing the degree of branching.展开更多
基金This work was supported by the National Natural Science Foundation of China
文摘Taking account of the effect ale heteroatoms iq backbone, this article dealt with the mean-square radii of gyration of polyalkyleneoxides by the approach of matrix algebra in accordance with the rotational isomeric state model, Numerical calculation with the parameters available in the literatures indicated that the dependence of [S-2] on the molecular weight can be expressed by the general formula: [S-2]=aM(b).
基金supported by the National Basic Research Program (973) of China (No.10574109)the Zhejiang Provincial Science and Technology Department (No.2007G60G1120019)+1 种基金National Science Foundation of Zhejiang Province (No.Y604064)Zhejiang Gongshang University (No.08-13),China.
文摘The mean-square radius of gyration <S^2>,the mean-square dipole moment <D^2>,the mean-square end-to-end distance <R^2> and their temperature coefficients of unsymmetrical disubstituted poly(methylphenylsiloxane) (PMPS) chains, as a function of stereochemical structure,confomational energies and length of polymers,were studied by using an improved configurational-confomational statistical method based on the rotational-isomeric-state theory.It is found that the increase in isotacticity of P...
基金This work was supported by the Deutsche Forschungsgemeinschall and der Chemischen Industrierate, Alexander von Humboldt Stiffeng and the China National Distinguished Young Investigator Fund (No. 29925413).
文摘Crystallization in polymer systems actually is a process that transfers the entangled melts into a semi-crystalline layered structure. Whether or not a chain disentangles may result in different crystallization mechanism. When compared to the crystal thickness (d(c)), the volume occupied by the chain in the melts i.e., the radius of gyration (R-g), plays a very important role in polymer crystallization. When d(c) less than or equal to R-g, crystallization does not necessitate a chain disentangling. The entanglements are just shifted into the amorphous regions. However, as d(c)>R-g, i.e., as the crystal thickness gets larger than the radius of gyration of the chain in the melt, it becomes necessary for a chain to disentangle. Then a change of crystallization mechanism occurs. Such change has been experimentally observed in the crystallization of poly(I-butene). A change in the crystal morphologies from spherulite to quadrangle, is seen via PLM, as crystallization temperatures increase. Even more, such a change is molecular weight dependent, and shifts to lower temperature as molecular weight decreases. There exists a jump of crystal thickness and crystallinity associated with morphological change, as seen via SAXS. A change of crystallization kinetics and crystallinity is further evidenced via dilatometry. The unique feature of P1b crystallization has been discussed based on the radius of gyration of chain in the melt (R-g), and very good agreement is obtained.
文摘This work deals with the dependence of the z-average mean-square radius of gyration (<R 2> z) on the degree of branching(DB) for highly branched copolymers made from the one-pot cocondensation of AB 2 and AB monomers. A new expression of the degree of branching has been derived. The DB monotonously increases with increasing A group conversion and the fraction of AB 2 monomers. The value of DB calculated in accordance with our formula is lower than that given by Frey and coworkers. Howerver, when the reaction approaches completion, our expression of the degree of branching degenerates into the equation reported by Frey. Furthermore, the z-average mean-square of gyration of the resulting copolymer in the Θ state has been derived on the basis of the classical work developed by Stockmayer, Gordon, Li and Ba. The relationship between DB and <R 2> z is illustrated by numerical results. The z-average mean-square radius of gyration of the copolymer with a certain weight-average molecular weight monotonously decreases with increasing the degree of branching.
