Flexibilised stryrene-N-substituted maleimide copolymers with enhanced entanglement density

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The iniferter technique in radical polymerization under UV and thermal conditions: a comparative study

UV and thermal polymerisations of styrene were carried out in the presence of conventional 'iniferters'. The mechanisms of the two methods were investigated and provided new insight into the livingness of the so-called iniferter technique. Chain extension polymerisations were performed using symmetrical iniferters to check the living character of this technique under UV and thermal polymerization conditions. In accordance with the work of Otsu, we have shown that polymerisation under UV irradiation initiated by iniferters proceeds via the classical iniferter living (controlled) mechanism. On the other hand, thermal polymerisations were predominantly controlled by the reversible addition-fragmentation chain transfer (RAFT) mechanism

Flexibilized styrene-N-substituted maleimide copolymers. II. Multiblock copolymers prepared from PTHF-based iniferters

This article describes the synthesis and molecular characterization of thermal polymeric iniferters, based on hydroxy-terminated poly(tetrahydrofuran) (PTHF), bearing thiuram disulfide groups along the chain. Thermal polymerization after the addition of styrene (S) and N-methylmaleimide (MI) to these PTHF-based polymeric iniferters yielded segmented PTHF (SMI-block-PTHF)n block copolymers that proved to have a single Tg. The multiblock copolymers were molecularly characterized by elemental analysis, IR, and NMR. The thermal stability, as checked by thermogravimetric analysis, proved to be good up to about 350 °C. A size exclusion chromatography/differential viscosity (DV) analysis showed that the molecular weights of the synthesized single-phase multiblock copolymers were sufficiently high (several times the estimated molecular weight between two adjacent entanglements) to determine the entanglement density from the rubbery plateau modulus, for which the method developed by S. Wu (J Polym Sci Part B: Polym Phys 1989, 27, 723-741) was applied. The entanglement density of flexibilized SMI proved to be about 20-25% higher than that of the nonflexibilized SMI. This increase is disappointing, and more work, based on the described concept, is required to achieve the desired enhancement of the toughness

The iniferter technique in radical polymerization under UV and thermal conditions: a comparative study

UV and thermal polymerisations of styrene were carried out in the presence of conventional 'iniferters'. The mechanisms of the two methods were investigated and provided new insight into the livingness of the so-called iniferter technique. Chain extension polymerisations were performed using symmetrical iniferters to check the living character of this technique under UV and thermal polymerization conditions. In accordance with the work of Otsu, we have shown that polymerisation under UV irradiation initiated by iniferters proceeds via the classical iniferter living (controlled) mechanism. On the other hand, thermal polymerisations were predominantly controlled by the reversible addition-fragmentation chain transfer (RAFT) mechanism

The iniferter technique in radical polymerization under UV and thermal conditions: a comparative study

UV and thermal polymerisations of styrene were carried out in the presence of conventional 'iniferters'. The mechanisms of the two methods were investigated and provided new insight into the livingness of the so-called iniferter technique. Chain extension polymerisations were performed using symmetrical iniferters to check the living character of this technique under UV and thermal polymerization conditions. In accordance with the work of Otsu, we have shown that polymerisation under UV irradiation initiated by iniferters proceeds via the classical iniferter living (controlled) mechanism. On the other hand, thermal polymerisations were predominantly controlled by the reversible addition-fragmentation chain transfer (RAFT) mechanism

Flexibilized styrene-N-substituted maleimide copolymers with enhanced entanglement density

High molecular weight poly(styrene-co-N-substituted-maleimide)-block-poly(tetrahydrofuran) multiblock copolymers with an excellent thermal stability were synthesized using the polymeric iniferter technique. Evidence for the existence of these multiblock copolymers was obtained by submitting them to gradient polymer elution chromatography and by snipping the chemical bonds between the SMI blocks and the PTHF blocks, after which the molecular weight distribution of the remaining SMI blocks was determined. Only one glass transition temperature was observed in a modulated temperature DSC scan of the segmented copolymers, typical for a homogeneous material. The T-g of these flexibilized, single-phase multiblock copolymers is still high enough to qualify them as engineering plastics. The entanglement density, which is closely related to the toughness of materials, of a styrene-N-phenylmaleimide copolymer flexibilized by 12 wt % PTHF was raised by a factor 1.6 as compared to the unflexibilized styrene-N-phenylmaleimide copolymer. These entanglement densities were deduced from the respective rubber plateau moduli, which were corrected for the nonentangled low molar mass fraction by applying the Wasserman-Graessley model

Controlled stereochemistry of polyamides derived from cis/trans-1,4-cyclohexanedicarboxylic acid

A series of copolyamides 12.y was synthesized either with y = 6, or 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) residue, or a mixt. of both. The influence of the synthetic route of 1,4-CHDA-contg. polyamides on the obtained cis-trans ratio of the incorporated 1,4-CHDA was investigated. The use of acid chlorides provided a synthetic route with full control of the cis-trans ratio of the 1,4-CHDA residue during synthesis, whereas synthesis at elevated pressure and temp. caused isomerization. The content and cis-trans ratio of 1,4-CHDA in the copolyamides were detd. by soln. 13C NMR spectroscopy. Increasing the degree of partial substitution of the adipic acid by 1,4-CHDA resulted in an increase in Tm, even for low molar percentages of 1,4-CHDA. This phenomenon points to isomorphous crystn. of both the 12.6 and 12.CHDA repeating units. The m.ps. of the synthesized polyamides were independent of the initial cis-trans ratio of 1,4-CHDA, provided that the samples were annealed at 300 Deg before DSC anal. The polyamides exhibited a different melting pattern depending on the 1,4-CHDA content. At a low 1,4-CHDA content a net exothermic recrystn. occurred during melting, whereas at higher contents of 1,4-CHDA this recrystn. occurs to a lesser extent, and 2 sep. melting areas are obsd