Most degradation processes are a result of oxidative  or thermal reactions or a combination of the two.  Low temperature degradation is usually a result of some oxidation process and may occur when components of the polymer backbone are particularly susceptible to oxidation.  Higher temperature processes are the result of thermal cleavage of bonds in the polymer backbone.  

The oxidative processes can sometimes be minimized by addition of stabilizers. Avoidance of Thermal degradation requires a backbone structure having bonds that are difficult to cleave (polyimides such as Kapton).  For some polymers degradation is initiated from the endgroups so that end-capped polymers may be more stable than those that have reactive chain ends.  

At low temperatures the degradatin of polimers proceeds with such low velocities that it is possible to say that their destruction has virtually no place. At high temperatures, the degradation proceeds with a noticeable speed. These speeds dependent on temperature  and type of polimer. In different areas the temperature may vary as the speed of the degradation and its mechanism. This means that can be allocated various low molecular weight products, wich can be seen on the mechanism of destruction.can be given when dealing with specific polimer.

Most degradation processes are a result of oxidative  or thermal reactions or a combination of the two.  Low temperature degradation is usually a result of some oxidation process and may occur when components of the polymer backbone are particularly susceptible to oxidation.  Higher temperature processes are the result of thermal cleavage of bonds in the polymer backbone.  

The oxidative processes can sometimes be minimized by addition of stabilizers. Avoidance of Thermal degradation requires a backbone structure having bonds that are difficult to cleave (polyimides such as Kapton).  For some polymers degradation is initiated from the endgroups so that end-capped polymers may be more stable than those that have reactive chain ends.  

Thermal polymer degradation is the breakage of molecular chain bonds by means of oxidative process or by heat . Thermal decomposition process can be accelerated by means of oxidants (air or oxygen). The minimum decomposition temperatures are lower in the presence of oxidants. This kind of thermal degradation is termed as low temperature thermal degradation. High temperature thermal degradation is a result of cleavage of thermal bonds when heated to elevated temperatures.

Jim Cella has given a very good answer. Most commercial polymers are completely stable thermally at 150C. They can degrade by oxidative cleavage of backbone bonds. This happens rapidly with unstabilized aliphatic polymers at 150C and slowly at normal temperatures. It is facilitated by exposure to ultraviolet light.

If you are looking to avoid degradation at "high" temperatures, a good way to prevent oxidation is to provide an inert environment (i.e. Nitrogen....). 

It is true that degradation at high temp is much quicker than at low temperatures but the mechanism is usually totally different. Compare degradation of an egg at 100C (hardens) and at 37 C (creating a chick) and at lower temp (rots). 

Normally at 150 Degree C Polymer is at its Melt Temperature, If it is under processing condition. Which is not called to be a degradation. But if it if under end use condition and undergoes 150 Degree C then the gravimetric loss will start, this can be by Radiation, thermal stresses or Environmental reasons. initially it can be observed by the yellowness, and then loss in weight.

At very high temp. there will be completely chain disintegration and sometimes polymer may char. It can be at above 300 Degree C for polymers.

At very low temp. the vander vaal forces (weak bonds) between the chains start disintegrating so first polymer becomes brittle and then starts losing weight. Normally we term it as “Low Temp. Brittlness”.

Hope the answer is satisfying your query, or otherwise you may specify the context of your study.  

at high temperature you can cleave almost all bonds in polymers.

at low temperature, the thermal degradation mechanism is driven by the radical oxidation of polymer

maybe you could tell us more about the polymer you are studying

 The two mechanisms of polymer degradation (oxidative process or thermal energy absorption) have difference in there own origin. Roughly it can be said, that the first one is a chemical process and the second one has a physical origin. The breakage of molecular chain bonds depends on many factors: Chemical structure, network formation, crystallinity, filler incorporation etc. So, the answer in your question is not a simple one. In any particular system a special treatment is needed. There are relevant papers. Good luck.