Physical properties increasing the sidechain length

Moving from the Cj and C2 sidechain polyhydroxyalkanoates to longer sidechains leads to a progressive change in the crystallinity and mechanical properties of the resulting copolymers. 

As the sidechain length increases, the level of crystallinity decreases significantly. These results compare with the PHB homopolymer (C4) with crystallinities in the range 60-70%. 

Crystal structure measurements on C8-C10 polymers indicate orthorhombic unit cells with P2i, 2, 2j, symmetry as seen for HB/HV systems. The fibre repeat distance, unit cell dimension, c, showed the greatest change and fell with increasing sidechain length. This may suggest that greater rotational freedom of movement is possible with the less constrained, longer sidechains. 

Slow crystallization rates were also reported for the long sidechain polyhy-droxyalkanoates. The glass transition temperature also decreased with increasing sidechain length. 

Marchessault and coworkers [29] have reported preliminary mechanical data for copolymers whose average monomer size was within the range Cg-C,o. Their 

---