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Title: Enhancement of polyester properties through molecular design
Author: Meehan, Stephen
Awarding Body: University of Reading
Current Institution: University of Reading
Date of Award: 2012
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The aim of the work described in this thesis was to develop novel semi-crystalline, semi-aromatic polyester-based materials with improved thennal properties relative to their parent polymers, specifically poly(ethylene terephthalate) (PET) and po)y(ethylene-2,6-naphthalate) (PEN). This work involved the design and development of a small-scale (2-10 g) vacuum polyesterification rig, synthesis of a variety of suitable comonomers - both known and unknown - and the synthesis of a range of novel copolymers by incorporating these comanomers through melt-phase polycondensation. Several comonomers were synthesised which could potentially enforce are-entrant chain-fold through confonnational restrict ions. However, these comonomers typically hindered the crystallisability of the copolymers and had no significant effect on Tg• Double Tgs were apparent for a small number of these copolymer compositions. A wide range of imide-containing comonomers was synthesised and incorporated into both PET and PEN. The resulting novel copoly(ester-imide)s generally displayed enhanced Tgs but showed a reduction in crystallinity at levels of 5 to 15 mol% diimide. Annealing of these copolymers gave materials with a greater Xc. often close to those of their respective homopolymers. The diimide monomer N,N-bis-(2-hydroxyethyI)pyromeJlitic diimide (POI), incorporated at 5 mol% into PEN, gave a Tg 10°C higher as well as a T m 10°C lowerthen PEN, with a comparable value of Xc once annealed. Finally, a range of copolymers containing 3,3',4,4'-biphenyldiimide units were introduced into PET, PEN and poly(butylene-2,6-naphthalate) (PBN). Crystallinity was observed for all compositions investigated with PEN (2-25% comonomer), and the degree of crystallinity and rate of crystallisation increased progressively above 5 mol%. X-ray powder and fibre diffraction techniques revealed that compositions containing ~ 5 mol% diimide, annealed at 180°C, have a completely different crystalline structure from PEN itself. The new unit cell for this novel copolymer is monoclinic, space group C2/m, with two chains passing through the unit cell, and cell parameters a = 10.50, b = 6.85, c = 13.28 A, f3 = 141.6°
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available